1. Field of the Invention
This invention relates to a new animal growth promotant. More particularly, it relates to a new animal feed composition which comprises an acyl peptide or its non-toxic salt as an effective ingredient, and to methods for promoting the growth of animals and improving the rate of weight gain of animals and improving the efficiency of feed utilization by animals, which comprises the oral administration of the animal feed composition comprising the acyl peptide or its non-toxic salt to animals.
2. Description of the Prior Art
The acyl peptide to be used in this invention is represented by the following formula (I). ##STR1## wherein R.sup.1 is lactoyl-alanyl-, R.sup.2 is carboxymethylamino, and R.sup.3 is carboxy; or
R.sup.1 is heptanoyl, R.sup.2 is 1-carboxyethylamino and PA1 R.sup.3 is carboxy; or PA1 R.sup.1 is stearoyl, R.sup.2 is 1-carboxyethylamino and PA1 R.sup.3 is hydrogen.
The acyl peptide (I) and its non-toxic salt to be used in this invention is the known one possessing an enhancing activity of immune response [cf. U.S. Pat. No. 4322341].
For many years, the animal science industry has tried to provide an animal growth promotant, and some antibiotics have been developed and used as such, including, for example, penicillins, tetracyclines, bacitracin, enramycin, virginiamycin or the like. The antibiotics used as animal growth promotants up to now are characterized by their strong antimicrobial activities, especially against Gram-positive bacteria. Accordingly, it has been a matter of common knowledge in the field of animal science that when an antibiotic is used as an animal growth promotant, the antibiotic may be preferably selected from the ones which possess antimicrobial activities, especially against Gram-positive bacteria.
However, the animal growth promotants available in the market, including such antibiotics, can not be said to be entirely sufficient in the actual application thereof to animals due to the occurrence of antibiotic resistant microorganisms and the like.